The present invention relates to a spot-type disc brake, in particular for automotive vehicles, which substantially comprises a brake support member fastened to the wheel axle and a brake caliper embracing the edge of a brake disc having a brake-actuating device and brake shoes to be pressed against the brake disc from either side when the brake is activated, the caliper being arranged on a guide element in a manner slidable parallel to the brake disc axis and the brake shoes being held by means of pins, screw bolts or the like.
Known floating-caliper disc brakes of this type include an opening provided in that portion of the brake caliper which is arranged above the circumference of the brake disc, the opening being sized at least to allow removal through it of worn brake shoes after detaching retaining pins and to enable insertion of new brake shoes, both the worn and new brake shoes comprising a pad carrier and a brake pad. In some cases it is not necessary to dismount the disc brake from the wheel for the replacement of the brake shoes. The frictional and braking forces are transmitted partly to the retaining elements, i.e. pins or screw bolts, in conjunction with expanding springs, partly, through marginal areas of the pads or pad carriers which abut against corresponding areas of the brake caliper, to the latter and from the caliper via the brake support member to the wheel axle. In this context, it is difficult to exclude an overload of the individual components due to the high braking forces at any condition of wear and to keep the forces low which are necessary to enable the caliper to slide.
It is also known to support the floating brake caliper in a slidable manner on two bolts arranged parallel to the disc brake axis at a radial distance from each other. The two bolts are fixed either directly to the wheel trunnion or to an element of the vehicle frame. In a known embodiment of this kind as disclosed in German Patent DE-Al 3,044,185 the brake caliper carriers only the external brake pad and is guided only by one of the two bolts. The internal brake pad arranged opposite is mounted on a supporting plate which slides on the second guide bolt during braking. When the brake is actuated, the hydraulic brake cylinder arranged at the internal leg of the brake caliper acts on the supporting plate. In addition, the internal supporting plate is connected with a guiding and force transmitting element which engages the brake caliper on the disc entry side as well as on the disc exit side, the connection being realized in such a manner that while a slide parallel to the brake disc axis is rendered possible, the circumferential force exerted on the supporting plate is, however, transmitted also to the brake caliper and through it in part to the second guide bolt. The circumferential or frictional forces are, thus, distributed to both guide bolts in a virtually uniform manner.
The use of two guide bolts entails a significant volume of manufacturing and assembly efforts. Moreover, it is difficult to align the guide bolts such that the braking forces are uniformly transmitted to the guide bolts permanently and at any wear condition of the pads which is necessary to prevent the bolts from canting or clamping in the slide bearing or an inadmissible increase of the necessary caliper sliding force.
A spot-type disc brake preferably intended for motorcycles which floats only on one guide bolt and is constructed as a pendulum-type caliper brake is also disclosed in German Patent DE-OS 28 39 195. The whole brake abuts against a supporting element arranged aside the brake disc, with the guide bolt which holds the brake on the supporting element being arranged roughly in the center of the supporting area. The brake shoes are retained in the brake caliper with the aid of an extended portion of the guide bolt and of a second, shorter bolt which exclusively extends through the brake caliper. The total circumferential or frictional forces must be absorbed by these two bolts. In this version, a uniform transmission of forces from the brake shoes to the retaining bolts, from the latter to the brake caliper and to the guide element as well as to the supporting areas is attainable, if at all, only in case of relatively low braking forces.